On Linux/x86_64, there are three ABIs that the kernel understands directly
(without qemu user):
- 64-bit, as produced by "gcc -m64",
- 32-bit (i686 code), as produced by "gcc -m32",
- 64-bit instructions with 32-bit pointers, as produced by "gcc -mx32".
The patch from 2020-06-15 "* config.guess (x86_64:Linux:*:*): Detect x32 ABI."
<https://lists.gnu.org/archive/html/config-patches/2020-06/msg00005.html>
added support for recognizing the third case (x32 ABI).
But it broke the second case (32-bit ABI), when a GCC version 9 or higher is
used.
$ CC="gcc-version 8.5.0 -m32" ./config.guess
x86_64-pc-linux-gnu
$ CC="gcc-version 9.4.0 -m32" ./config.guess
x86_64-pc-linux-gnux32
$ CC="gcc-version 10.3.0 -m32" ./config.guess
x86_64-pc-linux-gnux32
$ CC="gcc-version 11.3.0 -m32" ./config.guess
x86_64-pc-linux-gnux32
$ CC="gcc-version 12.1.0 -m32" ./config.guess
x86_64-pc-linux-gnux32
The reason is that the code tests for the __ILP32__ preprocessor symbol,
and this preprocessor symbol is defined also in the 32-bit ABI for GCC ≥ 9.
See:
$ : | gcc-version 8.5.0 -m64 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __x86_64 1
#define __LP64__ 1
#define __x86_64__ 1
#define _LP64 1
$ : | gcc-version 9.4.0 -m64 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __x86_64 1
#define __LP64__ 1
#define __x86_64__ 1
#define _LP64 1
$ : | gcc-version 8.5.0 -m32 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __i386 1
#define __i386__ 1
$ : | gcc-version 9.4.0 -m32 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __i386 1
#define __i386__ 1
#define __ILP32__ 1
#define _ILP32 1
$ : | gcc-version 8.5.0 -mx32 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __x86_64 1
#define __x86_64__ 1
#define __ILP32__ 1
#define _ILP32 1
$ : | gcc-version 9.4.0 -mx32 -E -dM - | grep '\(LP\|__.*86.* 1\)'
#define __x86_64 1
#define __x86_64__ 1
#define __ILP32__ 1
#define _ILP32 1
The config.guess of GCC 12.1.0 includes this change, and as a
consequence, I can no longer build 32-bit binaries of GCC without
specifying --build and --host options — something that worked in
the past.
Find here a patch that changes the output in the 32-bit ABI case
from
$ CC="gcc-version 8.5.0 -m32" ./config.guess
x86_64-pc-linux-gnu
$ CC="gcc-version 9.4.0 -m32" ./config.guess
x86_64-pc-linux-gnux32
to
$ CC="gcc-version 8.5.0 -m32" ./config.guess
i686-pc-linux-gnu
$ CC="gcc-version 9.4.0 -m32" ./config.guess
i686-pc-linux-gnu
This is similar to what config.guess already does for Linux/mips and Darwin.
It also fixes the problem I reported for CC="tcc" in
<https://lists.gnu.org/archive/html/config-patches/2021-03/msg00000.html>.
From 8de7981fd45505acfd4aa266290a5ec54a119ef3 Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Sun, 8 May 2022 19:08:08 +0200
Subject: [PATCH 1/2] config.guess (x86_64:Linux:*:*): Detect 32-bit ABI.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
* config.guess (x86_64:Linux:*:*): Test for the 32-bit ABI. Don't assume that
__ILP32__ is a certain indicator for the x32 ABI; for GCC ≥ 9 it no longer is.
---
config.guess | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/config.guess b/config.guess
index 7f76b62..f953bc9 100755
--- a/config.guess
+++ b/config.guess
@@ -4,7 +4,7 @@
# shellcheck disable=SC2006,SC2268 # see below for rationale
-timestamp='2022-01-09'
+timestamp='2022-05-08'
# This file is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
@@ -1151,16 +1151,24 @@ EOF
;;
x86_64:Linux:*:*)
set_cc_for_build
+ CPU=$UNAME_MACHINE
LIBCABI=$LIBC
if test "$CC_FOR_BUILD" != no_compiler_found; then
- if (echo '#ifdef __ILP32__'; echo IS_X32; echo '#endif') | \
+ if (echo '#ifdef __i386__'; echo IS_X86; echo '#endif') | \
(CCOPTS="" $CC_FOR_BUILD -E - 2>/dev/null) | \
- grep IS_X32 >/dev/null
+ grep IS_X86 >/dev/null
then
- LIBCABI=${LIBC}x32
+ CPU=i686
+ else
+ if (echo '#ifdef __ILP32__'; echo IS_X32; echo '#endif') | \
+ (CCOPTS="" $CC_FOR_BUILD -E - 2>/dev/null) | \
+ grep IS_X32 >/dev/null
+ then
+ LIBCABI=${LIBC}x32
+ fi
fi
fi
- GUESS=$UNAME_MACHINE-pc-linux-$LIBCABI
+ GUESS=$CPU-pc-linux-$LIBCABI
;;
xtensa*:Linux:*:*)
GUESS=$UNAME_MACHINE-unknown-linux-$LIBC
--
2.25.1
